1. Field
The present inventions relate generally to hearing devices and, for example, hearing devices that are worn entirely in the bony region of the ear canal for extended periods without daily insertion and removal.
2. Description of the Related Art
The external acoustic meatus (ear canal) 10 is generally narrow and contoured, as shown in the coronal view illustrated in FIG. 1. The adult ear canal 10 is axially approximately 25 mm in length from the canal aperture 12 to the tympanic membrane or eardrum 14. The lateral part of the ear canal 10, i.e., the part away from the tympanic membrane, is the cartilaginous region 16. The cartilaginous region 16 is relatively soft due to the underlying cartilaginous tissue, and deforms and moves in response to the mandibular or jaw motions, which occur during talking, yawning, eating, etc. The medial part of the ear canal 10, i.e., the part toward the tympanic membrane 14, is the bony region 18 (or “bony canal”). The bony region 18, which is proximal to the tympanic membrane 14, is rigid, roughly 15 mm long and represents approximately 60% of the canal length. The skin in the bony region 18 is thin relative to the skin in the cartilaginous region and is typically more sensitive to touch or pressure. There is a characteristic bend, which occurs approximately at the bony-cartilaginous junction 20, that separates cartilaginous region 16 and from bony region 18, commonly referred to as the second bend of the ear canal.
Debris 22 and hair 24 in the ear canal are primarily present in the cartilaginous region 16. Physiologic debris includes cerumen or earwax, sweat, decayed hair and skin, and sebaceous secretions produced by the glands underneath the skin in the cartilaginous region. Non-physiologic debris is also present and may consist of environmental particles, including hygienic and cosmetic products that may have entered the ear canal. The bony portion of the ear canal does not contain hair follicles, sebaceous, sweat, or cerumen glands. Canal debris is naturally extruded to the outside of the ear by the process of lateral epithelial cell migration, offering a natural self-cleansing mechanism for the ear.
The ear canal 10 terminates medially with the tympanic membrane 14. Lateral of and external to the ear canal is the concha cavity 26 and the auricle 28, which is cartilaginous. The junction between the concha cavity 26 and cartilaginous region 16 of the ear canal at the aperture 12 is also defined by a characteristic bend 30, which is known as the first bend of the ear canal. Canal shape and dimensions can vary significantly among individuals.
Extended wear hearing devices are configured to be worn continuously, from several weeks to several months, inside the ear canal. Such devices may be miniature in size in order to fit entirely within the ear canal and are configured such that the receiver (or “speaker”) fits deeply in the ear canal in proximity to the tympanic membrane 14. To that end, receivers and microphones that are highly miniaturized, but sufficiently sized to produce acceptable sound quality, are available for use is hearing devices. The in-the-canal receivers are generally in the shape of a rectangular prism, and have lengths in the range of 5-7 mm and girths of 2-3 mm at the narrowest dimension. Receivers with smaller dimensions are possible to manufacture, but would have lower output efficiencies and the usual challenges of micro-manufacture, especially in the coils of the electromagnetic transduction mechanism. The reduction in output efficiency may be unacceptable, in the extended wear hearing device context, because it necessitates significant increases in power consumption to produce the required amplification level for a hearing impaired individual. Examples of miniature hearing aid receivers include the FH and FK series receivers from Knowles Electronics and the 2600 series from Sonion (Denmark). With respect to microphones, the microphones employed in in-the-canal hearing devices are generally in the shape of a rectangular prism or a cylinder, and range from 2.5-5.0 mm in length and 1.3 to 2.6 mm in the narrowest dimension. Examples of miniature microphones include the FG and TO series from Knowles Electronics, the 6000 series from Sonion, and the 151 series from Tibbetts Industries. Other suitable microphones include silicon microphones (which are not yet widely used in hearing aids due to their suboptimal noise performance per unit area).
Recently introduced extended wear hearing devices are configured to be located in both the cartilaginous region 16 and the bony region 18 of the ear canal 10. A design exists for an extended wear hearing device intended to rest entirely within the bony region 18 and is disclosed in U.S. Patent Pub. No. 2009/0074220 to Shennib (“Shennib”). There are a number of advantages associated with the placement of a hearing device entirely within the ear canal bony region 18. For example, placement within the ear canal bony region 18 and entirely past the bony-cartilaginous junction 20 avoids the dynamic mechanics of the cartilagenous region 16, where mandibular motion, changes in the position of the pina, such as during sleep, and other movements result in significant ear canal motion that can lead to discomfort, abrasions, and/or migration of the hearing device. Another benefit of placement within the ear canal bony region 18 relates to the fact that sweat and cerumen are produced lateral to the bony-cartilaginous junction 20. Thus, placement within the bony region 18 reduces the likelihood of hearing device contamination. Sound quality is improved because “occlusion,” which is caused by the reverberation of sound in the cartilaginous region 16, is eliminated. Sound quality is also improved because the microphone is placed relatively close to the tympanic membrane, taking advantage of the directionality and frequency shaping provided by the outer parts of the ear, so that sound presented to the hearing device microphone more closely matches the sound that the patient is accustomed to receiving at their tympanic membrane.
Although conventional hearing devices that are configured to be placed entirely within the bony region 18 are an advance in the art, the present inventors have determined that they are susceptible to improvement. For example, the hearing device disclosed in Shennib has a core, which includes a power source, a microphone and a receiver that are located within a housing, and also has a pair of acoustic seals that engage the outer surface of the core housing and support the core within the ear. While Shennib teaches that a desirable length for such a hearing device (in the lateral-medial direction) is 12 mm or less, the present inventors have determined that there are other dimensional and acoustic issues which must be addressed, and that the configurations of conventional hearing devices do not address these dimensional and acoustic issues in a manner that will allow the hearing devices to both fit within the bony region in a significant portion (i.e., at least 75%) of the adult population and provide acceptable sound quality.
Other issues identified by the present inventors are associated with the batteries that power in-the-canal hearing devices. For example, the configuration of conventional hearing device batteries prevents batteries that have sufficient power capacity (measured in, for example, milliamp hours (mAh)) from being shaped in a manner that would enable an overall hearing device configuration which allows the hearing device to fit within the ear canal bony region in a significant portion of the adult population.
Zinc-air batteries (and other metal-air batteries) are frequently used in hearing devices because of their volumetric energy efficiency. Zinc-air batteries can be a challenge to design and manufacture because the cathode assembly must have access to oxygen (i.e., air) and the electrolyte solution, commonly a very slippery sodium hydroxide solution or potassium hydroxide solution, must be contained within the battery can without leaking. The conventional method of containing the electrolyte within the battery involves crimping the cathode assembly around an anode can with a sealing grommet between the two. Due to the challenges associated with mass production, the most common crimped battery is the button cell, which includes short, cylindrical anode and cathode cans that can be stamped (or drawn) and crimped uniformly. However, as noted in U.S. Pat. No. 6,567,527 to Baker et al. (“Baker”), button cells are not sufficiently volumetrically efficient to provide the capacity for an extended wear deep-in-canal (DIC) hearing device. Baker discloses a zinc-air battery that has a bullet-shaped anode can, with an oval cross-section, formed from a stainless steel clad material (bi-clad copper-steel or tri-clad copper-steel-nickel). Steel is the structural material, i.e., the material that provides the structural support for the anode can, and the inner surface is oxygen free copper. Implicit in the use steel for the structural material is the fact that the anode can is formed by a stamping or drawing process. With respect to the crimping process that secures the cathode assembly and anode can to one another and creates the seal at the grommet, Baker discloses the formation of an internal retention ledge on the inner surface of the anode can that opposes the crimp force. The internal retention ledge is formed by welding or brazing a retention ring into a step on the inner surface of the anode can. The retention ledge supports a sealing grommet against which the cathode assembly and cathode base are crimped by bending the anode can around the cathode base. Alternately, Baker teaches a retention ledge formed by collapsing a portion of the can inwardly with a bending (or “beading”) and crimping process.
Although the Baker anode cans are advantageous for a variety of reasons, the present inventors have determined that they are susceptible to improvement. For example, the amount of crimp force that may be employed to join the anode can and the cathode assembly, and create the seal, is limited by the amount of force that the internal ledges can withstand without cracking or bending. The bullet-shaped Baker anode cans must also be supported from below during the crimping process and, accordingly, the crimp force must not exceed the buckling strength of the bullet-shaped can. Baker discloses a battery (FIG. 13 of Baker) where an indented anode can is joined to the cathode by crimping the cathode around the indented anode portion, which would also require the drawn, beaded anode can to be supported by its body during the cathode crimping. The structure's ability to withstand crimp force would be limited. The present inventors have determined that, in some instances, the crimp force required to crimp the anode can and achieve the proper seal at the grommet is greater than the internal retention ledges within the can are able to withstand and/or results in buckling of the anode can. The present inventors have also determined that the drawing and stamping processes associated with conventional anode can manufacturing techniques undesirably limits anode cans to those which have relatively symmetric, smooth surfaces and relatively short throws.